“Always Measure Backward” is a core principle for living in The GAIN, which involves evaluating one’s current position against their starting point, rather than against a future ideal. This method of measurement is designed to create an immediate sense of progress, confidence, and happiness by focusing on tangible achievements.

Antifragile is the capacity to become better, stronger, and more capable through challenges and setbacks. Unlike resilience (resisting shocks) or robustness (staying the same), antifragility means one gets better, stronger, and more capable as a result of facing challenges and setbacks.

The GAP is a state of mind that results from measuring oneself or one’s situation against an ideal. Because ideals are by definition unreachable, living in this state creates perpetual feelings of unhappiness, frustration, and inadequacy, regardless of one’s actual accomplishments.

The GAIN is a state of mind that results from measuring oneself backward against their starting point. This perspective allows a person to appreciate their actual progress, which generates immediate feelings of happiness, confidence, and motivation. The book positions the GAIN as correcting the measurement error that produces the GAP: Where the GAP points the measure toward an unreachable ideal, the GAIN points it toward a concrete past self.

Harmonious passion is a healthy, intrinsically motivated form of passion where an individual controls the passion rather than being controlled by it. It enhances other areas of life and is driven by a “want” rather than a “need.”

The hedonic treadmill is a psychological phenomenon where people quickly adapt to positive changes, causing the thrill of achievement to wear off, leaving them feeling unfulfilled again. The book argues that measuring oneself in the GAP keeps a person perpetually stuck on this treadmill, always chasing the next ideal without finding lasting happiness.

Mental subtraction is a psychological exercise for increasing gratitude and appreciation. It involves imagining what life would be like if a positive relationship, achievement, or possession were taken away or had never existed, thereby highlighting its true value.

Obsessive passion is an unhealthy, impulsive form of passion fueled by unresolved internal conflicts. It is associated with a desperate “need” to achieve something to fill an internal void and can lead to addiction and tunnel vision.

Psychological flexibility is the ability to manage one’s emotions and move forward toward goals even when setbacks occur. This trait is developed by being in the GAIN, as it involves taking ownership of all experiences and transforming them into learning and growth rather than being derailed by them.

A reference point is the standard used for evaluation and comparison. The book distinguishes between external reference points (societal standards, other people’s achievements) which lead to the GAP, and internal reference points (one’s own past self) which are essential for being in the GAIN and becoming self-determined.

Self-determination is the state of having an internal reference point and defining success on one’s own terms. A self-determined person is intrinsically motivated and no longer measures themselves against external ideals or other people, which is a key outcome of living in the GAIN.

Success criteria is a personalized list of principles that define what being successful means for an individual in the present moment (e.g., “I know I’m being successful when…”). It creates an internal standard for making decisions and evaluating one’s life.

The authors’ term for the last hour before bedtime, the sweet spot of the day is considered the highest-leverage hour because actions such as reviewing daily wins and planning the next day can influence sleep quality, subconscious processing, and the focus and productivity of the following day.

The Experience Transformer® is a structured thought process for transforming any experience, positive or negative, into lessons, innovations, and breakthroughs. It involves asking a series of questions to extract value and learning from an event, thereby ensuring that all experiences contribute to future progress.